The effects of slow-wave sleep (SWS) deprivation and time of night on behavioral performance upon awakening

The aim of the present study is to evaluate the effects of selective SWS de privation on the motor and sensory motor performance impairment immediately after awakening from nocturnal sleep at different times of the night. Ten normal males slept for 6 consecutive nights in the laboratory: one adaptati on, two baseline, two selective SWS deprivation, and one recovery night. Du ring the last 4 nights performance was assessed four times: (a) before slee p, as a baseline measure; (b) within 30 s from the first nighttime awakenin g, after 2 h of sleep; (c) within 30 s from the second nighttime awakening, after 5 h of sleep; (d) within 30 s from the final morning awakening. Afte r each awakening, following a 3-min cognitive test, a simple Auditory React ion Time task (ART, about 5 min) and a Finger Tapping Task (MT, 3 min) were administered. Median of Reaction Times (RT) and of Intertapping Intervals (ITI), 10% fastest RT, 10% slowest RT, and number of misses were considered as dependent variables. The selective SWS deprivation was very effective: SWS percentage during both the deprivation nights was close to zero. This s trong manipulation of SWS amount interacted with time-of-night :factors in influencing sleep inertia. The SWS deprivation procedure caused a worsening of behavioral performance during the deprivation nights, as well as upon t he final awakening of the recovery night. Behavioral performance slowing up on awakening is accounted for by: (1) a general decrement in overall respon se speed (median of RT); (2) an "optimum response shift", i.e., a decrease in speed of the fastest responses; (3) an increase of lapsing, with more ma rked response delays resulting in a; further decrease in response speed in the "lapse domain". Finally, our results do not support the existence of a circadian rhythm of sleep inertia linked to body temperature rhythm. (C) 19 99 Elsevier Science Inc. All rights reserved.